Speech/USSD interoperability mechanism

ABSTRACT

A method for performing USSD transfer between a mobile station and a cellular communications network. The USSD transfer has a maximum data rate equal to the data rate of an associated control channel. The method comprises the following steps: 1) evaluating a set of factors in favor of the maximum data rate, for forming a totality of factors, the totality being at least partly independent of the existence of the associated channel prior to said evaluating; 2) comparing the totality of factors to a predetermined margin; and 3) performing the USSD transfer substantially at the maximum data rate in response to a positive result in said comparison, and otherwise at a lower data rate.

This application is the National Phase of International ApplicationPCT/FI99/00843 filed Oct. 13, 1999 which designated the U.S. and thatInternational Application was Published under PCT Article 21(2) inEnglish.

BACKGROUND OF THE INVENTION

The invention relates to improving the performance of USSD (UnstructuredSupplementary Service Data) transfer in a cellular communicationssystem, such as GSM (Global System for Mobile Communication).

The user of a mobile station (MS) can use USSD to give instructions tothe supporting PLMN (Public Land based Mobile Network). For example,incoming calls can be routed to number 123456 by dialling *21*#123456#.USSD is also one of the mechanisms for implementing new services. USSDallows an MS and a service application to communicate with each other bycharacter strings, in a way which is transparent to the MS and to theintermediate network elements. USSD can be used as a narrow-band bearerfor over-the-air (OTA) and value-added services (VAS) applications. Withrespect to a more detailed description of the USSD, reference is made tothe following ETSI GSM recommendations: GSM 02.90: European digitalcellular telecommunications system (Phase 2); Stage 1 description ofUnstructured Supplementary Service Data (USSD), GSM 03.90: Digitalcellular telecommunications system (Phase 2); Unstructured SupplementaryService Data (USSD)—Stage 2, and GSM 04.90: European digital cellulartelecommunications system (Phase 2); Unstructured Supplementary ServiceData (USSD)—Stage 3. USSD requests, notifications and responses containa USSD string, an alphabet indicator and a language indicator, asdefined in GSM 03.38.

USSD signalling may be initiated by the mobile station or by thenetwork. Phase 1 supports only MS-initiated USSD. Network-initiated USSDservice requires that all parts of the mobile communications system beat least phase 2 systems. The mobile communications network may at anytime send a USSD message to a mobile station MS registered with thenetwork in order to transmit information to the subscriber. Thisoperation may be either a request (asking the MS to provide information)or a notification (requiring no information to be provided by the MS).No prior provisioning of USSD is required, although provisioning ofservices which make use of USSD may be required.

According to the above ETSI recommendations, USSD signalling takes placebetween an MS and an MSC/VLR (Mobile services Switching Centre/VisitorLocation Register) or HLR (Home Location Register). USSD supports amaximum of 160 bytes of user data per message. (The upper limit can beless than 160 bytes depending on the underlying protocol layers.) UnlikeSMS (Short Message Service), USSD has no store-and-forwardfunctionality: mobile-terminated USSD messages are delivered to the MSimmediately, or the delivery fails (e.g. because the MS is unreachable).

For the purposes of this application, a GSM-type mobile station has twomodes: a call mode and an idle mode. A mobile station is in call mode ifand only if it is “in a call”, which state is defined in the GSMrecommendation 02.30.

According to the above ETSI recommendations, USSD transfer takes placeon two different channels depending on whether or not the MS is in callmode or idle mode. In call mode, Fast Associated Control Channel (FACCH)is used. In idle mode, Slow Dedicated Control Channel (SDCCH) is used.

The speed of the FACCH channel is approximately 140 bytes per second andthat of the SDCCH channel approximately 83 bytes per second. Thus, evenin idle mode, any USSD message can be delivered in less than twoseconds.

It is conceivable that the use of USSD for implementing value-added andover-the-air services will increase. In this case, especially ifmultiple consecutive USSD messages are needed, the slow transfer speedof the SDCCH channel could be seen as a problem. Also, prolonged use ofthe FACCH channel degrades the quality of speech on the associatedspeech channel. (It should be noted that for keeping the descriptioncompact, FACCH is used as a synonym for the fast channel, and SDCCH isused as a synonym for the slow channel. However, FACCH and SDCCH areterms used in the GSM system and its derivatives, but these terms arenot necessarily used in future cellular systems.)

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to study if thespeed of USSD in idle mode could be improved, and if yes, to provide amethod and equipment for improving the speed of USSD in idle mode.Another object of the present invention is to study if the degradationin speech quality due to prolonged use of the FACCH channel can beminimised. Yet another object is to develop a mechanism that isexpandable to accommodate future modifications. All these objects areachieved with a method and equipment which are characterized by what isdisclosed in the attached independent claims. Preferred embodiments aredisclosed in the attached dependent claims.

A straightforward way of improving the speed of USSD transfer would beto specify that all USSD transfers take place on the fast FACCH channel.This would, however, require changes in existing standardisation. Also,the FACCH is not a dedicated channel, but an associated one, which meansthat it is implemented by stealing bits from the associated speechchannel, if one exists. If such bit stealing is allowed to go onfrequently and for long periods of time, it will degrade speech qualityto some extent. On the other hand, if the mobile station is not in callmode, establishing the FACCH for the sole purpose of USSD transferrequires establishing a corresponding speech channel, which could beseen as a waste of radio resources. The user of the MS may not want topay extra for speeding up the USSD transfer and, if the network isheavily loaded, the operator may not want to allocate an extra speechchannel for the sole purpose of speeding up USSD transfer.

Similarly, a straightforward way of eliminating the degradation ofspeech quality would be to specify that all USSD transfers take place onthe slow SDCCH channel. This would, however, be a drastic solution.Moreover, in the current GSM system an SDCCH channel does not exist whenthe MS is in call mode.

The invention is based on locating the problem and finding a solutionfor it. The solution is based on an expandable concept that can beimplemented, at first, as a simple on/off mechanism, but which can beextended to balance the different needs and interests of the parties ofthe call as listeners, the MS user as a user of OTA and/or VASapplications, the network operator, and the other users of the network.

According to the invention, the degradation of speech quality islessened or totally eliminated by substantially lowering the data rateof the USSD transfer when necessary, in order to maintain adequatespeech quality.

The data rate can be lowered by using the dedicated control channelSDCCH, if one exists. In a GSM system and its derivatives, the SDCCHexists unless the mobile station is in call mode. If a dedicated controlchannel does not exist, the data rate can be lowered by dividing a longUSSD transfer into several consecutive USSD messages and delayingindividual USSD messages (by inserting gaps between them) until thedegradation of speech quality is brought to an acceptable level.

The expandable concept for performing USSD transfer can be implementede.g. by a method including at least the following steps:

(i) evaluating a set of factors in favour of the maximum data rate forforming a totality of the factors, the totality being at least partlyindependent of the existence of said associated channel prior to saidevaluating; and

(ii) using the totality of the factors to determine whether to performthe USSD transfer substantially at the maximum data rate or at a lowereddata rate.

Performing the USSD transfer substantially at the maximum data rateimplies that the FACCH channel will be used and that the data rate isnot lowered sufficiently to substantially improve the quality ofpossible simultaneous speech on the speech channel (the improvement dueto the lowered data rate is not clearly audible to a human ear).

In this context, the totality of factors means more or less the same asevaluating substantially all factors available to (i.e. known by) thedecision-making process. By giving different interpretations to the‘factors in favour of the maximum data rate’ the invention can beimplemented in an extendible manner.

The invention can be implemented in a very simple manner if the totalityof factors favouring the maximum data rate is a simple determinationthat a need for USSD transfer exists and an FACCH channel is availableor can be established.

The totality of the factors in favour of the maximum data rate can beused to determine the data rate by comparing the totality of the factorsto a predetermined margin and by performing the USSD transfersubstantially at the maximum data rate in response to a positive resultin the comparison. If the result of the comparison is negative, the USSDtransfer takes place at a lower data rate. Preferably, this meansperforming the USSD transfer on a dedicated control channel (SDCCH), ifone exists, and otherwise delaying individual USSD messages. The networkoperator can transmit to decision-making units, such as mobile stations,one or more elements affecting the comparison, such as the predeterminedmargin. For example, when the network load increases, the operator cantransmit a higher margin which would disfavour the use of the maximumdata rate. Such parameter(s) can be transmitted on a broadcast controlchannel, or as USSD or short message transmissions, as is well known tothose skilled in the art. Because the predetermined margin is comparedwith the factors favouring the maximum data rate, the same result isachieved if the network operator transmits one or more elementsaffecting these factors, as will be described later in more detail.

A more flexible implementation than a simple on/off approach is achievedif the totality of the factors is formed by weighing each factor with arespective weight and combining the results of the weighing. It is alsopossible to similarly evaluate another set of second (negative) factorsdisfavouring the maximum data rate. Such second, or negative, factorscould include a determination that the network is heavily loaded.However, this is not necessary, considering that all such negativefactors have an opposite positive factor (i.e. an absence of a negativefactor). For example, the opposite of a heavy load in the network is theavailability of radio resources.

Positive factors favouring the maximum data rate could comprise one ormore of the following:

1) the amount of data to be transmitted;

2) the availability of radio resources in the network;

3) the relative amount of silence on the speech channel;

4a) the length of time from the beginning of the call

4b) duration of continuous speech, i.e. the length of time from thelatest period of silence on the associated speech channel

5) the MS user's preference of USSD transfer over speech quality.

The availability of radio resources in the network should be considered,especially when there is no call going on between the mobile station andthe network. In such a case, USSD transfer is the only reason forestablishing a speech channel, which is necessary for establishing anFACCH. In a heavily loaded network, the operator can be reluctant toallocate a speech channel for the sole purpose of speeding up USSDtransfer. On the other hand, if there is a call going on, then using theFACCH does not consume any additional resources, but it does degrade thequality of speech to some extent.

The amount of data to be transmitted should be considered too. There islittle point in using the FACCH for very short transmissions.

The relative amount of silence on the speech channel could be consideredas well. Using the FACCH degrades the quality of speech to some extentbut this is of no consequence if there is currently no speech on thespeech channel. Considering that a call involves two parties, of whichusually only one speaks at any given moment, approximately 50 per centof the time the content of the speech channel does not consist of speechframes but silence indicators, known as SID (Silence Descriptor) framesin the GSM system. A base station subsystem BSS (a base station, basestation controller and/or a transcoder) could be modified to respond toan inquiry from an external node regarding the relative amount of SIDframes. It is to be expected that in future cellular systems, such asUMTS (Universal Mobile Telecommunications System), the elements of theBSS will be more deeply integrated into a Radio Network Controller RNC.Such integration facilitates implementing the invention in respect ofdetecting silence indicators on the speech channel.

A small relative weight could also be given to the length of time fromthe beginning of the call and/or from the latest period of silence onthe speech channel. This is because the beginnings of continuous speechare crucial for understanding. If the call has been going on for aminute or two and/or continuous speech has been going on for a fewseconds, the listener can much better tolerate the degradation of speechquality due to usage of the FACCH.

For the purpose of demonstrating the expandable nature of the invention,some additional factors will be presented near the end of thedescription.

An USSD transfer may consist of several separate USSD messages and itmay go on for several minutes. (Currently, its maximum duration islimited to 10 minutes.) During a long USSD transfer, the factorsfavouring (or disfavouring) the use of the FACCH may changeconsiderably. Thus it is preferable to repeat the evaluation betweensuccessive USSD messages, although not necessarily between every twomessages.

BRIEF DESCRIPTION OF THE DRAWINGS

The method and the equipment according to the invention will bedescribed in more detail by means of preferred embodiments withreference to the appended drawings, in which:

FIGS. 1 to 3 are signalling diagrams illustrating various mechanisms forestablishing a FACCH channel if one is not already active; and

FIG. 4 is a block diagram illustrating one embodiment of the invention;

FIG. 5 is a flow chart illustrating another embodiment of the invention;and

FIGS. 6 and 7 are timing diagrams illustrating preferred embodiments ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

Before various embodiments of the invention proper, several mechanismsfor establishing an FACCH channel will be described. These techniquesare described in reference 1. Since reference 1 was not public at thepriority day of the present application, its inventive subject matter isrepeated here, with reference to FIGS. 1 to 3 of the appended drawings.

The mechanisms described in reference 1 are based on the idea that theamount of USSD data is determined, and if the amount exceeds (or islikely to exceed) a predetermined threshold (i.e. for lengthy USSDtransmissions), the faster FACCH channel is activated by directing theMS into call mode. A simple way of accomplishing this is to perform anunsuccessful call attempt. Thus these mechanisms are also based on anovel interpretation of a call mode, as specified in theabove-referenced GSM recommendation 02.30, wherein the call mode isdefined as follows: A mobile station is in a call from the time thatsignalling related to the establishment or attempted establishment of amobile originated or mobile terminated call commences, and before thecall or call attempt ends, and (if applicable), the mobile equipment hasstopped generating tones related to this call to the user. Fooling theMS into call mode (by performing an unsuccessful call attempt) activatesthe faster FACCH channel for USSD transfer. However, it should be notedthat the mobile station is “in a call” as defined by ETSI GSM 02.30,whereby the novel mechanisms require no deviations from existingstandards. Thus the method and equipment according to the inventionsolve the problem of the prior art USSD transfer in an elegant manner.

The novel mechanisms are also based on determining the amount of USSDdata (i.e. the length of USSD transmission) and on using the FACCHchannel only for lengthy USSD transmissions. Performing the unsuccessfulcall attempt for short USSD transmissions would create unnecessarysignalling load, which is especially harmful at the air interface. Thissignalling load must be balanced against the savings in time provided bythe mechanism of the invention. For example, the FACCH could be usedonly if using it saves at least one second. Because the FACCH transferis approximately 1.7 times faster than SDCCH transfer, it saves about40% of the time needed by the SDCCH transfer. If it is required that atleast one second must be saved, a minimum length for an USSD messagewould be 250 bytes. This exceeds the length of a single USSD message. Inother words, performing the unsuccessful call attempt is useful onlywith multiple consecutive USSD messages (assuming 83 and 140 bytes persecond for the SDCCH and the FACCH, respectively, and a minimum savingof one second). Of course, it must be remembered that initiating theunsuccessful call attempt wastes a fraction of a second. Thus the logicfor initiating the unsuccessful call attempt should be placed at the topof the protocol stack, i.e. at the application layer. Otherwise thelogic will not know that multiple USSD messages are needed.

FIG. 1 is a signalling diagram illustrating mobile originated USSDtransfer. Time advances from top to bottom. A USSD dialogue between twoparties will be described. One of the parties is a mobile station MS andthe other one is a part or an element of a public land based mobilenetwork PLMN serving the MS. The MS can be a small handportable cellularradio telephone but the invention is best utilised if the mobile stationcomprises or is associated with data processing equipment. An example ofsuch a mobile station is the Nokia Communicator 9000. Another example isa general-purpose portable computer connected with a Nokia CellularDatacard to a cellular radio telephone with a suitable interface, suchas the Nokia 2110 or 8110. All Nokia equipment is available from NokiaMobile Phones, Finland.

In step 1-2 a mobile station MS in idle mode determines that the lengthof the USSD transfer exceeds a predetermined threshold, which could beapproximately 250 bytes. In step 1-4 the MS initiates a call attemptthat ultimately should fail. One way of achieving this is to call anon-existent number. Alternatively, the MS could call itself. (At somelater stage, the network PLMN will reply that the called subscriber doesnot answer, but this reply is not significant for understanding theinvention.) Steps 1-6 through 1-12 constitute a mobile originated USSDdialogue which is known per se. In step 1-6 the MS initiates the USSDdialogue by sending a BEGIN, INVOKE PROCESSUSSDREQUEST message to thenetwork. (The primed message 1-4′ will be explained later.) In step 1-8the network responds with a CONTINUE, INVOKEUSSDREQUEST message. In step1-10 the MS sends a CONTINUE, RESULT USSDREQUEST message. The symbol“N*” indicates that the dialogue can comprise multiple pairs of messages1-8 and 1-10. Finally in step 1-12, the USSD dialogue is terminated byan END, RESULT PROCESSUSSDREQUEST message from the network.

The primed message 1-4′ relates to an alternative embodiment of themobile originated USSD transfer, wherein the call attempt 1-4 is notperformed before message 1-6 but only after it. In this case, the callattempt is shown with reference number 1-4′. In other words, it is alsopossible for a mobile station to initiate the USSD dialogue in step 1-6before performing the call attempt in step 1-4′. Thus the steps 1-4′ and1-6 are not performed in numerical order.

The lower limit for activating the FACCH channel can be fixed, e.g.approximately 250 bytes (which corresponds to a saving of one secondover SDCCH). Alternatively, the lower limit can be an adjustable networkparameter which the network distributes by some suitable means, such asbroadcasting, short message service, multipoint transmission (in packetradio networks), etc.

FIG. 2 is a signalling diagram illustrating a simple embodiment of anetwork originated USSD transfer. Messages with identical referencenumbers to those in FIG. 1 have identical function and will not bedescribed again. Step 2-2 corresponds to step 1-2 but in this case thenetwork determines that the mobile station MS is in idle mode and thelength of the USSD transfer justifies the use of the faster FACCHchannel (i.e. it exceeds the lower limit). In step 2-4 the networkinitiates a call attempt. However, unlike in step 14 shown in FIG. 1,the network cannot call a non-existent number (obviously, because the MSwould not be alerted). Instead, the network can send the MS a PAGEmessage in step 2-4. Steps 2-6 through 2-12 constitute a networkoriginated USSD dialogue which is known per se. In step 2-6 the networkinitiates the USSD dialogue by sending a BEGIN, INVOKE USSDREQUESTmessage to the MS. The primed message 2-4′ relates to an alternativeembodiment wherein the PAGE message is sent after the message 2-6, likethe alternative setup message 1-4′ in FIG. 1. Messages 1-8 and 1-10 havealready been explained. In step 2-12, the USSD dialogue is terminated byan END message.

FIG. 3 is a signalling diagram illustrating a preferred embodiment of anetwork originated USSD transfer. The simple embodiment shown in FIG. 2involves a problem because the user of the MS may be confused by theunsuccessful call attempt. The preferred embodiment shown in FIG. 3eliminates this problem by converting a network originated call attemptto a mobile originated one. In step 3-2 the network PLMN sends the MS anindication that the MS must initiate a call setup procedure foractivating the FACCH channel. This indication can be embedded, forexample, inside a protocol-specific header or parameter in anappropriate WAP (Wireless Application Protocol) layer. In the embodimentshown in FIG. 3, this indication has been embedded in the BEGIN, INVOKEUSSDREQUEST message which was shown as step 2-6 in FIG. 2. In step 1-4the MS initiates an unsuccessful call attempt by sending a SETUPmessage. The remainder of the procedure is similar to the one describedin connection with FIG. 2.

The preferred embodiment of the network originated USSD transfer hasseveral advantages over the simple embodiment. For example, no specialcall setup routines are required in the network. Also, because the MSdoes not have to be paged call setup is faster and the user of the MS isnot alerted.

The above-described mechanisms for activating the FACCH channel requireneither hardware changes nor changes to existing GSM standards. They canbe implemented as software routines in a mobile station and/or thePublic Land-based Mobile Network PLMN. In the mobile station, thesoftware routine can be installed in the cellular telephone proper, orin the associated computer, if any. Installing the software routine inthe associated computer, if applicable, is advantageous in the sensethat such software has a better chance of knowing or predicting thetotal number of USSD messages that will follow, and their combinedlength. Alternatively, the software routine according to the inventioncan be installed in the cellular telephone proper but the associatedcomputer could give the software routine an indication that several USSDmessages are likely to follow and the FACCH channel should be activated.

In the PLMN, the novel mechanisms are preferably implemented in a moredistributed manner. The logic for determining if multiple USSD messageswill be needed must be placed near the actual application. Typicalnetwork elements for executing OTA and VAS applications include Mobileservices Switching Centres, USSD centres, Home Location Registers andVisitor Location Registers of cellular communications systems andService Control Points of intelligent networks. The logic for performingthe unsuccessful call attempt as described in connection with FIGS. 2and 3 is preferably installed in a Mobile services Switching Centre.Other possible locations include a BTS (Base Transceiver Station), a BSC(Base Station Controller), and/or an RNC (Radio Network Controller).

After the above description of various novel techniques for establishingan FACCH channel, the description of the present invention will nowcontinue, with reference to FIG. 4 of the appended drawings. FIG. 4 is ablock diagram illustrating one embodiment of the present invention.Although the embodiments of the invention are best implemented assoftware routines, some embodiments can very well be illustrated asweighing and summing circuits, artificial neurons, fuzzy logic, or thelike.

Input signals 41A to 46A represent the various factors favouring the useof the maximum data rate. Input signals 41B to 46B represent thecorresponding weights. Blocks 41C to 46C are the weighing circuits (e.g.multipliers) for weighing each input signal with a respective weight.The five first weighing circuits 41C to 45C with associated input andoutput signals have functions corresponding to the positive factors 1 to5 described earlier. The sixth multiplier 46, drawn in dashed lines,illustrates the capability for future expansion. The output signals 41Dto 46D of the weighing circuits are summed in a summer 47, the outputsignal of which (signal 48A) is compared by a comparator 48 with areference level Ref. If the signal 48A exceeds the reference level Ref,the output of the comparator 48 is high, which is interpreted as asignal for using the maximum data rate.

The network operator can control the usage of the maximum data rate e.g.by transmitting to the mobile station one or more of the following: thereference level Ref (i.e. the predetermined margin); the signal 42A (theavailability of network resources; and/or the relative weights 41B to46B.

A user can favour USSD transfer speed over speech quality by setting acorresponding parameter at the mobile station. Alternatively, thecorresponding functionality can be achieved by setting the correspondingparameter in the user's subscription profile in a network register, suchas the HLR. The network can use this parameter when calculating thereference level which it transmits to the mobile station. The networkcan also transmit the parameter to the mobile station if it isconsidered preferable to store such user preferences with thesubscription profile in a network register, instead of the mobilestation.

Although it may not be feasible to implement the invention as discreteweighing and summing circuits as shown in FIG. 4, the Figurenevertheless suggests alternative embodiments. One of them is anartificial neuron, preferably an associative neuron, which can also beimplemented by means of software routines. Such an artificialassociative neuron can be taught to associate different situations withdifferent outcomes and thus it can be taught when to use the maximumdata rate and when not to.

Probably the best way to implement the invention is by means of somekind of an artificial neuron circuit or fuzzy logic taught by a humanexpert. After the teaching of the system is completed, the results ofthe teaching can be distributed as neuron weights.

Describing fuzzy logic systems, however, is difficult (or “fuzzy”).Therefore, FIG. 5 shows another embodiment which can be described withrelative ease, in the form of a flow chart. In step 50 the length of theUSSD transfer is determined or estimated. If the length is less than apredetermined margin, such as approximately 500 bytes there is no needto use the FACCH (at this length, the FACCH saves approximately 2seconds over the SDCCH). Next, in step 51, the availability of an FACCHis tested. If there is no FACCH (i.e. the MS is not in call mode), instep 52 the availability of radio resources is determined. If radioresources are available in the network, in step 53 an FACCH isestablished, as described above in connection with FIGS. 1 to 3.Otherwise, the SDCCH will be used and the test ends.

If the MS is in call mode in step 51 (a FACCH is available), in step 54the user's preferences are tested. In test 54, the user has threechoices: he/she may favour USSD speed over speech quality 1) strongly,2) in some situations, when certain other conditions are met, or 3) notat all. If the user strongly favours USSD speed over speech quality, theremaining tests 55 and 56 are skipped and the process advances to step57. If the user does not favour USSD speed at all, the remaining tests55 and 56 are also skipped, and the process advances to step 58. If theuser's preference is between these two extremes, in step 55 it is testedwhether there is a break in speech (speech channel at the time mainlyconsists of silence indicators/SID frames instead of speech frames). Ifyes, the process advances to step 57. Otherwise, in step 56 it is testedwhether continuous speech has been going on for a certain time, such as2 seconds. If yes, then the listener can better tolerate the degradationin speech quality resulting from prolonged use of the FACCH, andconsequently, the process advances to step 57.

If the process advances to step 57, the FACCH channel will be used. Onthe other hand, if the process advances to step 58, a lower data ratewill be used. If the outcome of tests 51 and 52 are negative, then theSDCCH channel will be used. Otherwise, the USSD transfer takes place onthe FACCH channel but at a lower data rate, or the USSD transfer issuspended until the ongoing call has ended.

FIG. 6 is a timing diagram illustrating one embodiment of the invention.Graph 60 represents speech activity on the speech channel. Graphs 61 and62 represent USSD activity on the SDCCH and FACCH channels,respectively. Each spike on graphs 61 and 62 represent a separate USSDmessage.

In the scenario shown in FIG. 6, it is assumed that either the MS useror the network operator has chosen not to use the embodiment shown inconnection with FIGS. 1 to 3, i.e. a speech channel is not activatedonly for speeding up USSD transfer.

The USSD transfer is initiated at time T0. As no speech channel exists,the USSD transfer takes place on the SDCCH channel. At time T1 the MSenters call mode to establish a call. A speech channel now exists, andthe USSD transfer takes place on the FACCH channel. As shown in FIG. 6,the USSD spikes are more frequent after T1 than before T1. At time T2,speech is detected on the speech channel, and the USSD transfer isslowed down. In this example, it is slowed down by using every thirdopportunity for sending a USSD message (the USSD data rate is lowered bya factor of three). At time T3, silence is detected on the speechchannel, and the USSD transfer continues at full speed until time T4,when speech is again detected on the speech channel, and the USSDtransfer is slowed down. This time, however, the period of continuousspeech is longer (more than about two seconds), and at time T5, the USSDtransfer continues at full speed although there is simultaneous speechon the speech channel. At time T6, silence is detected on the speechchannel but it is of no consequence, since the USSD transfer alreadytakes place at full speed. Times T4′ to T6′ correspond to times T4 toT6, respectively, but in this case, it is determined that the call hasbeen going on for quite some time (e.g. for a minute or so). Therefore,the time difference between T4′ and T5′ is shorter than the timedifference between T4 and T5. In other words, if there is speech on theassociated speech channel, the USSD transfer is slowed down later in thecall for a shorter period than in the beginning of the call. At time T7the call ends, and the USSD transfer is continued on the SDCCH channeluntil time T8, when the USSD transfer ends.

FIG. 7 shows an advantageous variation of the embodiment shown in FIG.6. According to this advantageous variation, between times T5 and T6(and T5′ and T6′ respectively), the USSD transfer takes place at asomewhat reduced speed, e.g. by using every other opportunity forsending a USSD message (the data rate is lowered by a factor of two).Such a variation requires changes in the embodiments shown in FIGS. 4and 5. In the former, the single comparator 48 can be replaced with e.g.a quantifier logic which quantifies its input signal 48A into a numberof classes, each class representing a different data rate. In thelatter, the outcome 57 should be divided into multiple outcomes, e.g. bymoving test 55 after the block 57 and by performing the USSD transfer ata somewhat reduced speed if the result of test 55 is negative.

Alternatively, in the embodiment shown in FIG. 4, the comparator 48 canbe entirely omitted, and its input signal 48A can be used, afteroptional post-processing, for determining the USSD data rate. In otherwords, signal 48A is used as a “throttle” signal for the USSD data rate.

As described earlier, the invention involves evaluating a set of factorsin favour of the maximum data rate for forming a totality of the factorsand using the totality to determine the data rate to be used, e.g. bycomparing the totality to a predetermined margin. FIGS. 4 and 5illustrate two different interpretations of the totality. In FIG. 4, thetotality is the output 48A of the summer 47 which is compared with thereference level Ref. In the embodiment of FIG. 5, the totalitycorresponds to the decision line 59 which is the result of Booleanfunction formed by the tests 50, 51, 52, 54, 55 and 56. If the Booleanfunction corresponding to decision line 59 evaluates to True (i.e.exceeds the predetermined margin of False), the maximum data rate willbe used.

Prior art USSD transfer mechanisms have only a single, rigid rule forchoosing between the FACCH and the SDCCH: if an FACCH exists, it will beused. The present invention breaks this rigid rule by creating a conceptwhich is more flexible than the prior art mechanisms: if the totality offactors favouring the use of maximum data rate exceeds a predeterminedmargin, the maximum data rate will be used, and otherwise the data rateis at least lowered, possibly entirely stopped until an ongoing call hasended. According to a preferred embodiment of the invention, the FACCHcan be used even if it has to be established for the sole purpose ofspeeding up USSD transfer. Also, even if the FACCH exists, it may beused at a lowered data rate if it is determined that maximum use of theFACCH would lower the quality of simultaneous speech on the speechchannel.

The mechanism according to the invention is easily expandable byintroducing new factors favouring the use of maximum data rate asnecessary. One practical example of such new factors could be a factthat the parties of the call know each other and thus are better able totolerate a degradation in speech quality. If a call is to/from a numberwhich is stored in the memory of the mobile station, then the parties ofthe call probably know each other. The test whether or not the call isto/from such a familiar number (i.e. a number which is stored in thememory of the MS) can be easily added to the embodiments shown in FIGS.4 and 5. In the former, an additional multiplier is needed (shown asblock 46C) and in the latter, an additional test (not shown separately)is needed in or near the chain of tests 54 to 56.

The mechanism according to the invention is also more dynamic than theprior art mechanism. The network can at any time transmit to the mobilestation one or more elements affecting the comparison between thetotality of the positive factors and the predetermined margin. Forexample, the network may transmit the margin itself; one or more of theweights (see FIG. 4); and/or one or more factors to be weighed, such asan indication of the availability of radio resources in the network, orthe user's preference, if such preferences are stored in a subscriberregister in the network, and not in the mobile station.

The invention has been described, by way of example, in connection withthe GSM cellular system (Global System for Mobile Communication). Theinvention is equally applicable in connection with the derivatives ofGSM, such as DCS (also known as GSM 1800), and any digital mobilecommunications network supporting USSD transfer on a fast channel if amobile station is involved in a call, and otherwise on a slow channel.

REFERENCE

[1] Co-assigned Finnish patent application 981692F1, “USSD TransferMechanism”, filed on Aug. 3, 1998.

What is claimed is:
 1. A method for performing a USSD transferassociated with transmitting data between a mobile station and acellular communications network, the method comprising: evaluating a setof factors to determine a maximum data rate associated with a totalityof the factors, the totality being at least partly independent of anassociated channel prior to the evaluating; and using the totality ofthe factors to determine whether to perform the USSD transfer at themaximum data rate or at a lowered data rate.
 2. The method of claim 1,wherein an amount of data to be transferred by the USSD transfer exceedsa maximum length of one USSD message and the using of the totality offactors is repeated between successive USSD messages.
 3. The method ofclaim 1, further comprising performing the USSD transfer at the maximumdata rate or at the lowered data rate and wherein performing the USSDtransfer at the maximum data rate includes establishing a controlchannel associated with the USSD transfer if one does not exist prior tothe evaluating of the totality of factors.
 4. The method of claim 1,further comprising performing the USSD transfer at the maximum data rateor at the lowered rate and wherein performing the USSD transfer at thelowered rate includes performing the USSD transfer on a dedicatedcontrol channel, if one exists and, otherwise, delaying individual USSDmessages or temporarily preventing the USSD transfer.
 5. The method ofclaim 1, wherein the using the totality of factors includes comparingthe totality of the factors to a predetermined margin and selecting themaximum data rate in response to a positive result in the comparisonand, otherwise, selecting the lowered data rate.
 6. The method of claim1, wherein the evaluating the set of factors includes weighing each ofthe factors in the set of factors with a corresponding weight andcombining the results of the weighing.
 7. The method of claim 6, whereinthe set of factors includes the amount of data to be transmitted.
 8. Themethod of claim 6, wherein the set of factors includes an availabilityof radio resources in the network.
 9. The method of claim 6, wherein theset of factors includes a relative amount of silence on a speechchannel.
 10. The method of claim 9, wherein the set of factors includesa length of time from a beginning of a call and from a latest period ofsilence on the speech channel.
 11. The method of claim 6, wherein theset of factors includes a preference setting of a mobile station user.12. The method of claim 6, wherein the set of factors includes a lengthof time from a beginning of a call or from a latest period of silence onthe speech channel.
 13. The method of claim 1, further comprisingtransmitting at least one element affecting the comparison from thenetwork to the mobile station.
 14. The method of claim 13, wherein theat least one element affects a predetermined margin.
 15. The method ofclaim 13, wherein the at least one element affects a correspondingweight.
 16. A radio transmitter for performing a USSD transfer,associated with transmitting data between a mobile station and acellular communications network, the transmitter comprising: means forevaluating a set of factors to determine a maximum data rate associatedwith a totality of the factors, the totality being at least partlyindependent of an associated channel prior to the evaluating; and meansfor using the totality of the factors to determine whether to performthe USSD transfer the maximum data rate or at a lowered data rate.
 17. Aradio transmitter for performing a USSD transfer, associated withtransmitting data between a mobile station and a cellular communicationsnetwork, the transmitter comprising: an evaluator configured to evaluatea set of factors to determine a maximum data rate associated with atotality of the factors, the totality being at least partly independentof the existence of an associated channel prior to that evaluation; anda processor configured to use the totality of the factors to determinewhether to perform the USSD transfer substantially at the maximum datarate or at a lowered data rate.